Title: Tunable resistive pulse sensing and nanoindentation of pH-responsive expansile nanoparticles

Authors: Eva Weatherall; Thomas Loho; Michelle Dickinson; Aaron H. Colby; Mark W. Grinstaff; Geoff R. Willmott

Addresses: School of Chemical and Physical Sciences, Victoria University of Wellington, P.O. Box 600, Wellington, New Zealand ' Department of Chemical and Materials Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand ' Department of Chemical and Materials Engineering, The University of Auckland, Private Bag 92019, Auckland, New Zealand ' Departments of Chemistry and Biomedical Engineering, Boston University, Metcalf Center for Science and Engineering, 590 Commonwealth Ave, Boston, MA 02215, USA ' Departments of Chemistry and Biomedical Engineering, Boston University, Metcalf Center for Science and Engineering, 590 Commonwealth Ave, Boston, MA 02215, USA ' The MacDiarmid Institute for Advanced Materials and Nanotechnology; The Departments of Physics and Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand

Abstract: Experimental studies of pH-responsive expansile nanoparticles (eNPs) have been carried out using tunable resistive pulse sensing (TRPS) and nanoindentation. The eNPs are initially ∼200 nm in diameter, but increase in size owing to a compositional change resulting from cleavage of pH-labile protecting groups on the polymer backbone at low pH. TRPS detected expected changes in the size of eNPs, most clearly through an increase in the size distribution close to ∼1 μm diameter with time after exposure to pH 5.0 electrolyte. Heavily cross-linked nanoparticles and eNPs kept at neutral pH did not produce such pronounced changes. Nanoindentation results demonstrate that for accurate measurement of eNP mechanical properties, particles must be precisely located and securely fixed to the substrate. Moreover, the expanded eNPs may be too weak to respond to conventional nanoindentation. Nanoscale physical characterisation of soft matter is of burgeoning importance in medical and biotechnological research and applications.

Keywords: expansile nanoparticles; eNPs; drug delivery; tunable resistive pulse sensing; TRPS; particle size distribution; nanoindentation; soft nanomechanics; nanotechnology; pH.

DOI: 10.1504/IJNT.2017.082426

International Journal of Nanotechnology, 2017 Vol.14 No.1/2/3/4/5/6, pp.446 - 456

Published online: 20 Feb 2017 *

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